Magnesium-mediated intramolecular reductive coupling: A stereoselective synthesis of C2-symmetric 3,4-bis-silyl-substituted adipic acid derivatives

Article abstract of DOI:10.1039/b910784c

Chiral C₂-symmetric 3,4-bis-silyl-substituted adipic acid derivatives have been synthesised by a Mg/trimethylsilyl chloride-mediated intramolecular reductive coupling of symmetrical disiloxanes of β-silylacrylic acid N-oxazolidinone derivatives

Full text of DOI:10.1039/b910784c

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Magnesium-mediated intramolecular reductive coupling: a stereoselective
synthesis of C2-symmetric 3,4-bis-silyl-substituted adipic acid derivatives†
Pintu K. Kundu and Sunil K. Ghosh*
Received 2nd June 2009, Accepted 7th August 2009
First published as an Advance Article on the web 14th September 2009
DOI: 10.1039/b910784c
Chiral C2-symmetric 3,4-bis-silyl-substituted adipic acid derivatives have been synthesised by a
Mg/trimethylsilyl chloride-mediated intramolecular reductive coupling of symmetrical disiloxanes of
b-silylacrylic acid N-oxazolidinone derivatives. Efficient and short syntheses of enantiomerically pure
enantiomers of 2,6-dioxabicyclo[3.3.0]octane-3,7-dione have been achieved from the bis-silylated adipic
acid derivatives using Fleming–Tamao oxidation as the key step.
a,b-unsaturated esters linked by a tether underwent reductive
coupling–Dieckmann condensation leading to bicyclic oxacy-
clopentanecarboxylate with varying degrees of preference for the
cis or trans ring junction products, depending upon the olefin
geometry, tether length and reaction conditions.13 Using reagents
other than SmI2, some recent reports14-21 have shown that the
intramolecular reductive coupling of a,b-unsaturated carbonyl
compounds joined by a suitable tether led to cyclic systems with
preferential formation of the trans-diastereoisomers. Magnesium
in methanol can induce intramolecular reductive cyclisation of
ketones17 tethered to activated olefins. The same combination
has been used18,19 for activated olefins connected by a tether to
give cyclic products with 3- and 5-membered rings, associated
with varying quantities of double bond reduction products. The
diastereoisomer ratio in the products depended on the substituents
at the activated olefins and the tether. In most cases, it varied
between 1.1 and 2.8, favouring the trans-isomers. Electroreductive
cyclisation15 of a bis-enoate tethered by a propyl chain has been
reported to give a 1,2-disubstituted cyclopentane system with
moderate to high trans-selectivity depending upon the proton
source.15d The chrysene radical anion-induced intramolecular
reductive cyclisation16 of bis(enone) led to a cis ring junction
preferentially. Photocatalysts in combination with sacrificial elec-
tron donors have also been developed20 for photoinduced electron
transfer to the b-position of a,b-unsaturated esters and ke-
tones. The resulting carbon-centred radicals led to intramolecular
C–C bond formation providing 5- or 6-membered rings with a
strong preference for trans-1,2-stereochemistry. The tin hydride21
induced intramolecular reductive cyclisations of a,b-unsaturated
ketones with electronically deficient olefins also favoured high
trans-selectivity.
Introduction
Molecules containing two (or more) stereochemically defined
silicon-bearing centres and terminal functionalities are useful
intermediates in organic synthesis. A silicon group can effect
stereochemical control1 in a 1,2-related and a 1,3-related fashion.
Therefore, molecules with two adjacent silicon-bearing centres can
effectively control stereocentres which are 1,4-related and beyond.2
Highly stereoselective syntheses of the meso diastereoisomer of
3
3,4-bis-silylated adipates by a SmI2 induced hydrodimerisation
of b-dimethyl(aryl)silylacrylates have been reported4 and used in
the stereocontrol of 1,4-related centres to achieve the synthesis of
both enantiomers of nonactic acid as well as nonactin.5 Thus,
the C2-symmetric racemic diastereoisomer of 3,4-bis-silylated
adipate is also expected to be a starting point for syntheses
of complex molecules. Besides, C2-symmetric molecules have
privileged structures with high potential for the generation of
molecular species suitable for asymmetric catalysis. Herein, we
report our successful approach to the stereoselective syntheses of
chiral C2-symmetric 3,4-bis-silyl-substituted adipic acid deriva-
tives and the utility of some of these intermediates for short
and efficient syntheses of enantiomerically pure enantiomers of
2,6-dioxabicyclo[3.3.0]octane-3,7-dione.
Results and discussion
Besides electrochemical methods,6 intermolecular reductive hy-
drocoupling of a,b-unsaturated carbonyl compounds is known
to be mediated by metals like Na,7 Yb8 and Sm9 or reducing
agents like SmI2 and TiCl4–Zn.11 Amongst these, SmI2, which
10
is frequently used for this purpose, can induce hydrodimerisation
of b-aryl/alkyl acrylic acid derivatives to give 3,4-diaryl/alkyl-
substituted adipates/adipamides12 in favour (66–100%) of the
C2-symmetric diastereoisomer. However, the same hydrodimerisa-
tion of b-silylacrylic acid esters3 favoured the meso diastereoisomer
(76–100%). An intramolecular version of this reaction with bis-
We, therefore, decided to resolve our problem of making
C2-symmetric racemic diastereoisomer 1 by using a five-membered
ring formation (Scheme 1). This can be expected to be achieved
Bio-Organic Division, Bhabha Atomic Research Centre, Mumbai, India.
E-mail: ghsunil@barc.gov.in; Fax: +91-22-25505151; Tel: +91-22-
25595012
† Electronic supplementary information (ESI) available: Copies of 1H and
13C spectra of new compounds. See DOI: 10.1039/b910784c
Scheme 1 Retrosynthesis of cyclic disiloxane 1.
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4611–4621 | 4611
©

View Article Online
by intramolecular reductive cyclisation of symmetrical disiloxane
tethered bis-acrylates 2 (X = OR¢).
Our first task was, therefore, to make the symmetric disiloxane
2a (R = Me, X = OMe), as syntheses of these types of molecule are
not known. Recently, we have reported22 the synthesis of vinylsi-
lanols and vinyldisiloxanes from dimethyl(phenyl)vinylsilanes by
a selective proteodephenylation using trifluoromethanesulfonic
(TfOH) or trifluoroacetic acid (TFA). We were pleased to see
that under these conditions, the silylacrylate 3a gave the desired
disiloxane 2a in excellent yield (Scheme 2). It is worth mentioning
that sometimes the product is contaminated with a small amount
of silanol 4a, which either on standing or treatment with a sub-
stoichiometric amount of potassium tert-butoxide gets converted
to the desired disiloxane 2a.
Scheme 4 Mg/TMSCl mediated reductive coupling of 2a.
product 5a and some unidentified oligomeric materials. We then
modified the procedure by adding the disiloxane 2a to the
mixture of Mg and TMSCl in DMF under various conditions
as presented in Table 1. Under all these conditions, the formation
of the double bond reduction product 5a (10–24%) could not
be avoided. The role of TMSCl in this reaction was manifold.
Without it, the reaction did not take place in DMF.‡ Therefore,
the presence of TMSCl accelerated the redox process between
Mg and the disiloxane substrate. Its presence also increases
the chemoselectivity of the reaction in favour of the reductive
cyclisation products over the double bond reduction product.
This can be explained by the mechanism proposed in Scheme 5.
The reductive cyclisation process was probably accelerated by
quenching the radical anion, formed by electron transfer from Mg
to the substrate 2a, with TMSCl to give the radical 6. This radical
underwent intramolecular conjugate addition to the unsaturated
Scheme 2 Synthesis of disiloxane 2a.
The intramolecular reductive cyclisation of the disiloxane 2a
was then attempted with SmI2 in THF–DMPU following the
literature3 procedure without much success. Moreover, SmI2 is
reactive to certain carboxylic acid derivatives such as N-acyl
oxazolidinones,23 highly air-sensitive and requires THF as a co-
solvent. While searching for a cheaper and more environmentally
friendly reagent, we found that Mg metal and SmI2 have similar
reduction potentials.24 Magnesium has already been used in
reductive reactions involving unsaturated esters as well as in
intramolecular reductive cyclisations.18,19 When we carried out the
reductive cyclisation of disiloxane 2a with Mg metal in dry MeOH
following the protocol of Chavan and Ethiraj,19 only the double
bond reduced product 5a (Scheme 3) was isolated. The reaction
did not proceed at all in solvents like THF, acetonitrile or DMF
even after prolonged stirring at room temperature.
Scheme 3 Reaction of 2a with Mg in MeOH.
Recently, Nishiguchi et al.25 have shown that in the presence
of trimethylsilyl chloride (TMSCl) as an additive, the Mg metal-
promoted reductive dimerisation of a,b-unsaturated aldehydes
and ketones in DMF generates bis-(silyl enol) ethers with very
high regioselectivity. We were gratified to note that the reaction
with disiloxane 2a under the reported conditions,25 took place with
complete consumption of starting material (Scheme 4; Table 1,
entry 1). Analysis of the crude product by 1H NMR spectroscopy
revealed the formation of a mixture of diastereoisomeric cyclic
products, cis-1a and trans-1a, along with the double bond reduced
Scheme 5 Proposed mechanism for reductive cyclisation of disiloxane 2a
promoted by Mg/TMSCl.
‡ The reaction did not proceed at all in solvents like THF and acetonitrile
even in the presence of TMSCl.
4612 | Org. Biomol. Chem., 2009, 7, 4611–4621
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
Table 1 Reductive cyclisation of disiloxane 2a promoted by Mg/TMSCl
Entry
Mg/TMSCl (equiv.)
Conc. of 2a in DMF
Temp (◦C)/addition time
Ratio of productsa cis-1a: trans-1a: 5a
Yield (%)b
1
2
3
4
5
6
7
8
12/12
12/6
100 mM
100 mM
12 mM
15 mM
8 mM
10 mM
30 mM
15 mM
28/1 min
0/10 min
28/3 h
10/3 h
28/5 h
10/1 h
0/1.3 h
28/3 h
42:40:18
43:40:17
39:40:21
42:38:20
46:30:24
52:30:18
42:42:16
63:27:10
25
70
75
75
80
80c
87
85d
12/12
12/24
24/24
12/12
12/12
12/6
a Obtained from 1H-NMR spectrum of the crude product. b Isolated combined yield of cis-1a, trans-1a and 5a. c Reaction performed under sonication.
d SmI3 (0.2 equiv.) was added as an additive.
ester functionality and finally one more electron addition gave the
intermediate anion 7 which was then quenched by TMSCl to give
bis silyl ketene acetal 8. The silyl acetal 8 underwent hydrolysis
during aqueous work-up conditions and provided the diester 1a.
By this process, TMSCl also protected the reductive cyclisation
product from further reactions like Dieckmann condensation or
oligomerisations.
Our next attempt was to improve the relative stereochem-
istry (trans/cis) as well as control the absolute configuration
during the cyclisation to obtain the trans-isomer(s) in pure and
enantiomeric form. It was envisaged that instead of an ester,
the Mg/TMSCl-mediated coupling of the corresponding amide,
possessing a suitable chiral amine, might be useful for this
purpose. Amongst the amides, chiral oxazolidinones,29 initially
introduced by Evans et al.30 are widely used as chiral auxiliaries.
These oxazolidinones, when attached to carboxylic acids, control
the diastereoselectivity31 of reactions at the position a to the
carboxylic acid group. Oxazolidinones are also known for their
strong directing effect32 on the conjugate addition of nucleophiles
to the b position of unsaturated acid derivatives and in elec-
troreductive hydrodimerisation.33 Sibi et al.34 have shown that
various oxazolidinone derivatives of a,b-unsaturated carboxylic
acids can control the stereoselectivity of C–C bond formation
at the b-position in radical reactions. Unlike alkyl amides, the
oxazolidinone amide bond is easily hydrolysed to give acids. In
view of all of this, we prepared the (S)-valine derived oxazolidinone
derivative of b-silylacrylic acid 10a as shown in Scheme 7. The
trans-b-silylacrylic ester 3a was hydrolysed to the acid 11a, which
was converted to the intermediate acid chloride by reacting with
oxalyl chloride, which was then reacted with the lithium salt of
Evans’ oxazolidinone 12a to give the oxazolidinone derivative
10a in high yield. Reaction of this amide 10a with TfOH (3.6
equiv.) in dichloromethane at -10 ◦C, followed by quenching with
ammonium hydroxide, produced the disiloxane 13a in very good
yield.
Next, we subjected the disiloxane 13a to the optimised reductive
cyclisation conditions (Table 1, entry 7) described for disiloxane
2a, using Mg/TMSCl in DMF at 0 ◦C, which led to complete con-
sumption of the starting material. Interestingly, the crude reaction
product showed the formation of a mixture of diastereoisomeric
cyclic products, cis-14a and two trans-products (trans-14a:trans-
15a = 60/40) with a strong preference for the desired trans isomers
(trans:cis = 85/15) (Scheme 8 and Table 2, entry 1). Also, the
formation of the double bond reduced product was significantly
reduced (not seen in the 1H-NMR spectrum of the crude product).
The isolated yield of the cyclic products was also very high (85%),
and the trans-isomers could be easily separated from the cis-14a
by crystallisation. Notably, even the two diastereoisomeric trans-
14a and trans-15a could be individually isolated by fractional
crystallisation with nearly quantitative recovery. To see the effect of
SmI3 in the reductive cyclisation, the reaction was also carried out
using disiloxane 13a, TMSCl and SmI3 (0.2 equiv.) as an additive
The stereoselectivity of the cyclisation was marginal in all these
conditions as shown in Table 1. A catalytic amount of SmI2 or
SmI3 and a stoichiometric amount of a reducing agent like Mg
can induce various types of reactions on carbonyl compounds
including pinacol type self couplings26 or couplings with activated
olefins.27 Being a lanthanide, samarium in the trivalent state is
known to be a good complexing agent28 and thus can activate
the substrate as well as make the transition state compact for
a better stereocontrol. Therefore, we were interested to see the
effect of SmI3 in this coupling reaction and a marginal preference
for cis-1a was observed when SmI3 (0.2 equiv.) was added to the
above reagents (Table 1, entry 8). The optimised conditions for the
cyclisation were therefore to use 12 equiv. each of Mg and TMSCl
in DMF with a 30 millimolar concentration of the unsaturated
ester 2a at 0 ◦C which gave a mixture of cis-1a, trans-1a and
reduced diester 5a in 87% isolated combined yield (Table 1, entry
7). Although little selectivity in the cyclisation was observed, the
formation of the reduction product was substantially reduced (1a:
5a = 84/16) under the optimised conditions. Racemic trans-1a is a
crystalline solid and easily crystallises out from a hexane solution
of the crude reaction product leaving behind the cis-1a and the
reduced product 5a in the solution, which were then separated by
chromatography.
The stereochemistry of the cyclic products was confirmed by
converting the known3 meso diester 9a to the cis-1a (Scheme 6).
For this, the meso diester 9a was briefly treated with TfOH
in dichloromethane at -4 ◦C and quenched with ammonium
hydroxide to provide cis-1a. By comparing the 1H NMR spectra,
the stereochemistry of the crystalline product from the Mg-
mediated reaction was confirmed to be the racemic trans-1a.
Scheme 6 Confirmation of stereochemistry.
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4611–4621 | 4613
©

View Article Online
number of research groups35-37 had independently introduced 5,5-
disubstituted oxazolidin-2-ones, called ‘SuperQuats’, as chiral
auxiliaries mainly to obviate the problems viz. purification of
products by crystallisation, and limit endocyclic cleavage during
removal, whichis knowntobe problematic withEvans’oxazolidin-
2-one 12a.30 We were specifically interested to see the effect of
5,5-disubstituted oxazolidin-2-ones on the reductive cyclisation
because we had already seen a dramatic improvement in diastere-
oselective anhydride opening38 when using them. We prepared
4-isopropyl-5,5-diphenyloxazolidin-2-one 12b and 4-isopropyl-
5,5-diaryloxazolidin-2-one 12c from (S)-valine following the re-
ported procedures.38,39 The lithium salts of the oxazolidin-2-ones
12b, 12c were made in THF using n-BuLi at 0 ◦C and reacted with
the intermediate acid chloride generated from acid 11b (obtained
from the hydrolysis of 3b) at -78 ◦C in THF to give the amides 10b
and 10c, respectively. The TolMe2Si group was chosen in these
cases because this group is expected to proteodearylate under
milder conditions compared to the PhMe2Si group. This was es-
sential to prevent degradation of the oxazolidinone moieties in 10b
and 10c. Unlike amide 10a, the conversion of the amides 10b and
10c to the corresponding disiloxanes 13b and 13c was performed
with less TfOH (2.5–3 equiv.) and at a lower temperature (-15 ◦C)
(Scheme 9). Reductive cyclisation of disiloxane 13b, under the
conditions described for amide 13a, resulted in the formation of
a mixture of diastereoisomeric cyclic products, cis-14b and two
diastereoisomeric trans-products (trans-14b: trans-15b = 45/55)
with a marginally higher preference for the desired trans-isomers
(trans: cis = 88/12) (Table 2, entry 3). Similarly, the disiloxane 13c
also gave a mixture of cis-14c and two diastereoisomeric trans-
products (trans-14c: trans-15c = 45/55) on reductive cyclisation
with Mg and TMSCl. Fractional crystallisation then provided
pure trans-15b or trans-15c but other isomers viz. cis-14b or cis-14c
and trans-14b or trans-14c could not be separated by crystallisation
or chromatography.
Table 2 Mg/TMSCl promoted reductive cyclisation of oxazolidinone-
attached disiloxanes 13a–13c
Cyclised products
Entry
Disiloxane
trans:cisa
trans-14: trans-15
%Yieldb
1
2
3
4
13a
13a
13b
13c
85:15
67:33
88:12
87:13
60:40
53:47
45:55
45:55
85
75c
83
83
a Obtained from1H-NMR spectrum of the crude product. b Combined
isolated yield of all isomers. c SmI3 (0.2 equiv.) was used as an additive.
To establish the absolute stereochemistry of the individual
trans-diastereoisomers viz. trans-14a and trans-15a, each of these
was converted to known bislactone 16. For this, trans-14a was
subjected to Fleming–Tamao40,41 oxidation using KHF2–H2O2 in
1/1 THF–MeOH at 60 ◦C (Scheme 10). Besides conversion of
the silyloxy groups to hydroxyl groups, the oxazolidinone group
was also removed under these conditions to give the intermediate
dipotassium salt. At this stage, a simple extraction of the reaction
mixture with ethyl acetate gave back the oxazolidinone 12a (90%)
and acidification of the residue gave the dilactone (-)-16. The
Scheme 7 Synthesis of disiloxane 13a.
under the above conditions. This reduced the trans/cis ratio to
67/33, with a marginal change in the selectivity between the trans-
isomers (Table 2, entry 2).
For further improvement in stereoselectivity, we decided
to modify the oxazolidin-2-one with various substituents. A
Scheme 8 Reductive cyclisation of disiloxane 13a.
4614 | Org. Biomol. Chem., 2009, 7, 4611–4621 This journal is
The Royal Society of Chemistry 2009
©

View Article Online
Scheme 9 Synthesis of disiloxanes 13b,c and their reductive cyclisation.
c 0.785, H2O for the antipode). Similarly, the minor trans-15a gave
(+)-2,6-dioxabicyclo[3.3.0]octane-3,7-dione (+)-1642 as confirmed
25
from the specific rotation data of (+)-16 ([a]D = +142.1, c 0.38,
H2O) (lit.:42 [a]D = +143 2.5, c 0.785, H2O), thus confirming its
19
(3R,4R)-configuration.
Interestingly, the major trans-diastereoisomers containing
‘SuperQuat’ oxazolidinones, trans-15b and trans-15c, after
Fleming–Tamao oxidation gave (+)-2,6-dioxabicyclo[3.3.0]-
octane-3,7-dione (+)-16. The marginal difference in stereocontrol
behaviour between oxazolidinones 12a and 12b or 12c is probably
due to the steric crowding caused by the 5,5-diaryl groups in
12b or 12c. It is important to note that the bis-lactone 16 has
been shown to be a useful intermediate in the synthesis of some
important biologically active compounds such as eldanolide,43
the Geissman-Waiss lactone,44 prostaglandin analogues,45 trans-
laurediols,46 8,9-epoxyeicosatrienoic acid47 and enantiomerically
pure butenolides.48 However, in spite of the significant utility of
the bis-lactone 16, to our knowledge, only two reports20f,48 are
available for the asymmetric synthesis of the (+)-16 and none for
(-)-16.
Conclusions
In conclusion, we have successfully developed a Mg/TMSCl-
mediated intramolecular reductive cyclisation of symmetric
disiloxanes made from chiral oxazolidinone derivatives of
b-silylacrylic acid to give C2-symmetric trans-diastereoisomers
with high stereoselectivity; however, the stereocontrol is marginal
amongst the trans-diastereoisomers. The trans-diastereoisomers
attached to Evans’ oxazolidinones were easily separated from the
cis-diastereoisomer and individual trans-diastereoisomers were
also separated by fractional crystallisation with ease and high
Scheme 10 Synthesis of dioxabicyclo[3.3.0]octane-3,7-diones.
(3S,4S)-configuration of the silicon-bearing asymmetric centres
in trans-14a was confirmed from the specific rotation data of
23
19
(-)-16 ([a]D = -145.3, c 0.64, H2O) (lit.:42 [a]D = +143 2.5,
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4611–4621 | 4615
©

View Article Online
recoveries. The individual isomers of cyclic products containing
“SuperQuat” oxazolidinones were difficult to separate.
(2 C), 165.3 (2 C); m/z (EI) 287 (M - 15, 30%), 233 (18), 179
(100), 163 (60), 149 (68), 133 (53), 119 (24), 73 (18).
1,1,3,3-Tetramethyl-1,3-di-[(2-methoxycarbonyl)ethyl]-
disiloxane 5a
Experimental
General methods
Magnesium turnings (101 mg, 4.1 mmol) were added to a stirred
solution of the diester 2a (125 mg, 0.41 mmol) in dry methanol
(6 mL) at room temperature under an argon atmosphere. After
4 h, the reaction mixture was poured into cold aqueous HCl
(0.3 N, 30 mL) and extracted with ethyl acetate. The extract was
dried over MgSO4 and evaporated under reduced pressure. The
residue was quickly filtered through a plug of silica gel to give
the diester 5a (103 mg, 82%) as a colourless oil; Rf 0.67 (hexane-
EtOAc, 90:10); nmax (film)/cm-1 2954, 2900, 1742, 1437, 1353, 1255,
1212, 1162, 1125, 1051, 843, 793; dH(200 MHz; CDCl3) 0.05 (12
H, s, 4 ¥ SiMe), 0.83 (4 H, t, J 8.4, 2 ¥ Me2SiCH2), 2.27 (4 H, t,
J 8.4, 2 ¥ CH2CO2Me), 3.64 (6 H, s, 2 ¥ CO2CH3); dC(50 MHz;
CDCl3) 0.0 (4 C), 13.1 (2 C), 27.9 (2 C), 51.5 (2 C), 175.3 (2 C);
m/z (EI) 291 (M - 15, 3%), 219 (75), 163 (100), 145 (74), 133 (45),
119 (13). 89 (15), 73 (15).
Compounds 3a,49 3b,3 9a3 and 12a–12c30,38,39 were prepared follow-
ing the published procedures. DMF was dried over CaH2 followed
by storage over 4 A molecular sieves. Mg turnings were purified
˚
by washing with dilute hydrochloric acid then water followed
by washing with acetone and dried under vacuum. TMSCl was
distilled over CaH2 before use. n-BuLi (~1.6 M in hexanes) was
purchased from Aldrich and its strength was determined by
titration prior to use. Trifluoromethanesulfonic acid, KHF2, H2O2
(30%), KOBut and oxalyl chloride were used as received from
commercial sources.
1H NMR and 13C NMR spectra were recorded on Bruker
200/500 MHz spectrometers. Spectra were referenced to residual
chloroform (d 7.25 ppm, H; 77.00 ppm, 13C). Chemical shifts
are reported in ppm (d); multiplicities are indicated by s (singlet),
d (doublet), t (triplet), q (quartet), quint (pentet), m (multiplet)
and br (broad). Coupling constants, J, are reported in Hertz.
C, H and N analyses were performed at the Indian Institute
of Technology, Mumbai and at the Hydrometallurgy Division,
BARC, Mumbai. High resolution mass spectra were recorded at
60–70 eV on a Waters Micromass Q-TOF spectrometer (ESI,
Ar). Optical rotations were measured in a JASCO DIP 360
polarimeter. Infrared spectra (IR) were recorded on a JASCO
FT IR spectrophotometer in NaCl cells or in KBr discs. Peaks
are reported in cm-1. Melting points (mp) were determined on
a Fischer John’s melting point apparatus and are uncorrected.
Analytical thin-layer chromatography was performed using home
made silica gel plates (about 0.5 mm).
1
Reductive cyclisation of 2a to give trans-1a, cis-1a and 5a
Freshly distilled TMSCl (5.2 mL, 41 mmol) was added to a stirred
suspension of magnesium turnings (1 g, 41 mmol) in dry DMF
(95 mL) at room temperature under an argon atmosphere. After
30 min, the reaction mixture was cooled on an ice-water bath and
a solution of disiloxane 2a (1 g, 3.3 mmol) in dry DMF (15 mL)
was added slowly over 1.3 h to the stirred reaction mixture. After
the addition was over, the reaction mixture was stirred for 5.5 h
and the cold bath was removed. The reaction mixture was allowed
to warm to room temperature (about 30 min) and poured into
cold saturated sodium bicarbonate solution and then extracted
three times with 10% ethyl acetate-hexane. The organic extract was
washed with brine, dried over anhydrous MgSO4 and evaporated.
The residue was purified by column chromatography on silica
using benzene-EtOAc (99:1) as eluent to give the reduction product
5a (125 mg, 12%) as a colourless liquid, the trans-1a (380 mg, 38%)
as a colourless solid, and the cis-1a (375 mg, 37%) as a colourless
liquid.
1,1,3,3-Tetramethyl-1,3-di-[(2-methoxycarbonyl)ethenyl]-
disiloxane 2a
Trifluoromethanesulfonic acid (4.8 mL, 54.6 mmol, 5.5 equiv.)
was added to a stirred solution of (E)-methyl 3-dimethyl-
(phenyl)silylpropenoate 3a (2.2 g, 10 mmol) in dry
dichloromethane (70 mL) at -4 ◦C. The reaction mixture
was stirred for 20 min at that temperature, poured slowly into a
stirred ice-cold aqueous ammonia solution (25%, 230 mL) and
extracted with chloroform. The organic extract was washed with
brine, dried over anhydrous MgSO4 and evaporated. The residue
was dissolved in THF (7 mL) and potassium tert-butoxide (8 mg,
0.07 mmol) was added. The reaction mixture was stirred at room
temperature overnight, diluted with water and extracted with
ethyl acetate. The organic extract was washed with brine, dried
over anhydrous MgSO4 and evaporated. The residue was purified
by column chromatography on silica using hexane-EtOAc (95:5)
as eluent to give the disiloxane 2a (1.3 g, 86%) as a colourless
liquid. Rf 0.64 (hexane-EtOAc, 90:10); nmax (film)/cm-1 3033,
2956, 2904, 2844, 1731, 1601, 1436, 1308, 1273, 1257, 1227, 1192,
1170, 1054, 998, 844, 802, 702; dH(200 MHz; CDCl3) 0.20 (12 H, s,
4 ¥ SiMe), 3.75 (6 H, s, 2 ¥ CO2CH3), 6.25 (2 H, d, J 19.0, 2 ¥
Data for trans-1a: mp 99–100 ◦C (from hexane); Rf 0.60 (hexane-
EtOAc, 90:10); (Found: C, 47.18; H, 8.08. C12H24O5Si2 requires C,
47.33; H, 7.94%); nmax (KBr)/cm-1 3005, 2985, 2956, 2899, 2856,
1731, 1436, 1421, 1357, 1306, 1250, 1205, 1176, 1145, 1052, 930,
873, 841, 789; dH(200 MHz; CDCl3) 0.09 (6 H, s, 2 ¥ SiMe), 0.24
(6 H, s, 2 ¥ SiMe), 0.86-1.10 (2 H, m, 2 ¥ Me2SiCHCH2), 2.22 (2
H, dd, J 15.8 and 10.6, 2 ¥ Me2SiCHCHAHB), 2.65 (2 H, dd, J
15.8 and 3.6, 2 ¥ Me2SiCHCHAHB), 3.64 (6 H, s, 2 ¥ CO2CH3);
dC(50 MHz; CDCl3) -2.5 (2 C), 0.6 (2 C), 27.0 (2 C), 35.4 (2 C),
51.5 (2 C), 174.2 (2 C); m/z (EI) 289 (M - 15, 7%), 245 (10), 231
(56), 179 (10), 163 (100), 149 (23), 133 (92), 119 (23), 73(46).
Data for cis-1a: (Found: C, 47.49; H, 7.95. C12H24O5Si2 re-
quires C, 47.33; H, 7.94%); Rf 0.51 (hexane-EtOAc, 90:10); nmax
(film)/cm-1 3021, 2954, 2917, 2848, 1738, 1437, 1356, 1254,
1204, 1164, 1114, 924, 847, 794, 758; dH(200 MHz; CDCl3)
0.14 (6 H, s, 2 ¥ SiMe), 0.18 (6 H, s, 2 ¥ SiMe), 1.60-
1.73 (2 H, m, 2 ¥ Me2SiCHCH2), 2.30 (2 H, dd, J 15.8 and
9.4, 2 ¥ Me2SiCHCHAHB), 2.46 (2 H, dd, J 15.8 and 6.2,
=
CH CHCO2CH3), 7.12 (2 H, d, J 19.0, 2 ¥ CH=CHCO2CH3);
dC(50 MHz; CDCl3) -0.3 (4 C), 50.9 (2 C), 133.9 (2 C), 146.5
4616 | Org. Biomol. Chem., 2009, 7, 4611–4621
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
2 ¥ Me2SiCHCHAHB), 3.65 (6 H, s, 2 ¥ CO2CH3); dC(50 MHz;
CDCl3) -1.4 (2 C), 0.2 (2 C), 23.8 (2 C), 31.8 (2 C), 51.7 (2 C),
174.2 (2 C); m/z (EI) 289 (M - 15, 9%), 231 (54), 179 (15), 163
(100), 149 (22), 133 (63), 119 (16), 73 (28). This compound was
also prepared in 65% yield from diester 9a following the procedure
for the preparation of disiloxane 2a.
was added into the reaction mixture and extracted with ether. The
extract was washed successively with saturated aqueous sodium
bicarbonate and brine, dried over anhydrous MgSO4, filtered and
concentrated under reduced pressure. The residue was purified by
column chromatography on silica using hexane-EtOAc (93:7) as
eluent to give the pure amide 10a (21.2 g, 92%) as a colourless solid.
(Found: C, 64.16; H, 7.58; N, 4.38. C17H23NO3Si requires C, 64.32;
H, 7.30; N, 4.41%); mp 59–60 ◦C (from hexane); [a]D +78.52
25
(E)-3-[Dimethyl(phenyl)silyl]propenoic acid 11a
(c 1.08 in EtOH); Rf 0.53 (hexane-EtOAc, 85:15); nmax (CHCl3)/
cm-1 3070, 3049, 2963, 2876, 1781, 1683, 1592, 1487, 1428, 1364,
1337, 1254, 1207, 1116, 1060, 974, 860, 819, 774; dH(200 MHz;
CDCl3) 0.45 (6 H, s, 2 ¥ SiMe), 0.88 (3 H, d, J 7.2,
CHMeAMeB), 0.92 (3 H, d, J 7.2, CHMeAMeB), 2.33-2.49 (1 H,
m, NCHCHMe2), 4.18-4.32 (2 H, m, NCO2CH2CH), 4.44-4.51
(1 H, m, NCHCHMe2), 7.33-7.40 (3 H, m, Ar), 7.50 (1 H, d, J
A solution of sodium hydroxide (15 M, 30 mL, 450 mmol) in
water was added portionwise to a stirred solution of (E)-methyl
3-[dimethyl(phenyl)silyl]propenoate 3a (32.5 g, 147.5 mmol) in 1,4
dioxane (580 mL). Ethanol (20 mL) was added to the reaction
mixture to make it homogeneous and it was then stirred overnight.
The solvent was removed under reduced pressure, diluted with
water (300 mL) and extracted with ether. The aqueous phase
was acidified with citric acid (pH ~ 4) and extracted with ethyl
acetate. The organic extract was washed with brine, dried over
anhydrous MgSO4 and evaporated to give acid 11a (29 g, 95%)
as a thick gum. nmax (film)/cm-1 3500-2500 (br), 3070, 3022, 2959,
1696, 1594, 1427, 1411, 1300, 1253, 1117, 997, 938, 843, 822, 732,
700; dH(200 MHz; CDCl3) 0.44 (6 H, s, 2 ¥ SiMe), 6.28 (1 H, d,
=
18.7, CH CHCON), 7.47-7.60 (2 H, m, Ar), 7.70 (1 H, d, J 18.7,
=
CH CHCO); dC(50 MHz; CDCl3) -3.3 (2 C), 14.6, 17.9, 28.3,
58.5, 63.3, 127.9 (2 C), 129.3, 133.7 (2 C), 133.9, 136.4, 148.8,
153.8, 164.2; m/z (EI) 302 (M - 15, 43%), 240 (17), 230 (31), 216
(60), 202 (90), 189 (46), 161 (54), 145 (55), 135 (100), 105 (40), 75
(26), 69 (42).
=
=
J 18.8, CH CHCO2H), 7.34-7.54 (6 H, m, CH CHCO2H, Ar).
dC(50 MHz; CDCl3) -3.4 (2 C), 128.0 (2 C), 129.5, 133.7 (2 C),
134.5, 135.8, 150.7, 171.0; m/z (EI) 206 (M+, 9%), 205 (32), 191
(32), 163 (25), 145 (21), 135 (26), 121 (28), 105 (19), 75 (100), 69
(25).
1,1,3,3-Tetramethyl-1,3-di-{2-[3-(4S)-3-carbonyl-4-isopropyl-2-
oxazolidinone]ethenyl}disiloxane 13a
Trifluoromethanesulfonic acid (13.8 mL, 157 mmol, 2.5 equiv.)
was added to a stirred solution of 10a (20 g, 63 mmol) in dry
dichloromethane (400 mL) at -10 ◦C. After 1 h, another portion
of TfOH (6 mL, 68.3 mmol, 1.1 equiv) was added to the reaction
mixture and it was stirred under the same conditions for 1 h.
The reaction mixture was poured slowly into a stirred ice-cold
aqueous ammonia solution (25%, 1.4 L) and stirred for 2.5 h.
The reaction mixture was extracted with chloroform and the
extract was washed with brine, dried over anhydrous MgSO4 and
evaporated under reduced pressure. The residue was purified by
column chromatography on silica using hexane-EtOAc (85:15) as
eluent to give the disiloxane 13a (13.5 g, 86%) as a colourless
solid. (Found: C, 53.34; H, 7.62; N, 5.77. C22H36N2O7Si2 requires
C, 53.20; H, 7.31; N, 5.64%); mp 87–88 ◦C (from hexane-EtOAc);
(E)-3-[Dimethyl(tolyl)silyl]propenoic acid 11b
Following the procedure for the preparation of 11a, (E)-ethyl
3-[dimethyl(tolyl)silyl]propenoate 3b (12.5 g, 50.3 mmol) gave
acid 11b (8.9 g, 80%) as a crystalline solid. mp 78–80 ◦C (from
hexane); nmax (KBr)/cm-1 3500-2500 (br), 3066, 3011, 2968, 2921,
1697, 1611, 1402, 1298, 1247, 1110, 1001, 935, 838, 795, 777;
dH(200 MHz; CDCl3) 0.40 (6 H, s, 2 ¥ SiMe), 2.35 (3 H, s, Ar-
=
Me), 6.25 (1 H, d, J 18.8, CH CHCO2H), 7.19 (2 H, d, J 7.6,
=
Ar), 7.39 (2 H, d, J 7.6, Ar), 7.46 (1 H, d, J 18.8, CH CHCO2H);
dC(50 MHz; CDCl3) -3.3 (2 C), 21.4, 128.9 (2 C), 132.2, 133.8 (2
C), 134.4, 139.5, 151.1, 171.2; m/z (EI) 220 (M+, 11%), 219 (14),
205 (51), 177 (28), 159 (25), 149 (22), 135 (25), 91 (22), 75 (100),
69 (24).
23
[a]D +93.1 (c 1.01 in EtOH); Rf 0.72 (hexane-EtOAc, 70:30);
n
max (CHCl3)/cm-1 3020, 2964, 2877, 1781, 1683, 1487, 1388, 1365,
1337, 1256, 1208, 1120, 1098, 1060, 840, 756; dH(200 MHz; CDCl3)
0.25 (12 H, s, 4 ¥ SiMe), 0.89 (6 H, d, J 7.8, 2 ¥ CHMeAMeB),
0.93 (6 H, d, J 7.8, 2 ¥ CHMeAMeB), 2.33–2.49 (2 H, m, 2 ¥
NCHCHMe2), 4.18-4.34 (4 H, m, 2 ¥ NCO2CH2CH), 4.44-4.51 (2
(4S)-3-trans-(2-Dimethylphenylsilyl)acryloyl-4-isopropyl-2-
oxazolidinone 10a
=
Dry DMF (0.03 mL, 0.38 mmol) was added to a stirred solution
of acid 11a (15 g, 72.7 mmol) in dry dichloromethane (100 mL)
and the reaction mixture was cooled in an ice-water bath. Oxalyl
chloride (25.4 mL, 291 mmol) was added and the reaction mixture
was allowed to attain to room temperature. After 3.5 h, the
solvent and volatiles were removed under reduced pressure to
give the crude acid chloride which was dissolved in dry THF
(68 mL). The acid chloride solution was added into a stirred
solution of lithium salt of oxazolidinone at -78 ◦C which was
prepared from oxazolidinone 12a (9.4 g, 72.7 mmol) and n-BuLi
(48.5 mL, 1.5 M solution in hexane, 72.7 mmol) in dry THF
H, m, 2 ¥ NCHCHMe2), 7.28 (2 H, d, J 18.6, 2 ¥ CH CHCON),
7.67 (2 H, d, J 18.6, 2 ¥ CH CHCON); dC(50 MHz; CDCl3) 0.3
=
(2 C), 0.4 (2 C), 14.7 (2 C), 18.0 (2 C), 28.4 (2 C), 58.6 (2 C), 63.4
(2 C), 133.4 (2 C), 148.7 (2 C), 153.9 (2 C), 164.5 (2 C); m/z (EI)
481 (M - 15, 19%), 324 (16), 261 (22), 260 (100), 186 (19), 157 (41),
133 (22), 69 (15).
Reductive cyclisation of 13a to give trans-14a, trans-15a and
cis-14a
Following the procedure for the intramolecular reductive cyclisa-
tion of disiloxane 2a, disiloxane 13a (7 g, 14.1 mmol), magnesium
turnings (4.1 g, 168.8 mmol) and TMSCl (21.4 mL, 168.8 mmol)
gave a mixture of trans-14a, trans-15a and cis-14a (6 g, 85%).
◦
(136 mL) at -78 C. The reaction mixture was stirred under the
same conditions for 30 min followed by 15 min in an ice-water
bath. A saturated aqueous ammonium chloride solution (600 mL)
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4611–4621 | 4617
©

View Article Online
The mixture was dissolved in ethyl acetate and the trans isomers
were precipitated out by adding hexane into the solution. The
mixture was filtered to give a solid mixture of trans-14a and
trans-15a (3.9 g, 55%) and the filtrate was evaporated to give a
gummy mixture containing all three isomers (2.1 g, 30%). The
solid mixture was crystallised from benzene-hexane to give pure
major trans-14a product (2.1 g, 30%) followed by crystallisation of
the residual mass from hexane-ethyl acetate to give minor trans-
15a (1.4 g, 20%). Separation of isomers by chromatography was
not easy because of very similar Rf values. A pure sample of cis-
14a for characterisation purposes was obtained by careful column
chromatography of the gummy residue containing mixture of all
isomers.
Found: MH+ 499.2275, C22H39N2O7Si2 requires MH+ 499.2290;
m/z (ES)521 (M + Na, 69%), 499 (M + H, 100), 481 (26), 370 (19),
279 (41), 132 (16).
(4S)-3-trans-(2-Dimethyltolylsilyl)acryloyl-5,5-diphenyl-4-
isopropyl-2-oxazolidinone 10b
Following the procedure for the preparation of 10a, (E)-3-
[dimethyl(tolyl)silyl]propenoic acid 11b (1.06 g, 4.8 mmol), ox-
azolidinone 12b (1.36 g, 4.8 mmol) and n-BuLi (3.2 mL, 1.5 M
solution in hexane, 4.8 mmol) gave N-substituted oxazolidinone
10b (2.06 g, 89%) as a crystalline solid. (Found: C, 75.02; H,
6.78; N, 2.91. C30H33NO3Si requires C, 74.50; H, 6.88; N, 2.90%);
mp 105–107 ◦C (from hexane-EtOAc); [a]D -163.95 (c 1.03 in
25
Data for trans-14a: (Found: C, 52.95; H, 7.85; N, 5.88.
C22H38N2O7Si2 requires C, 52.98; H, 7.68; N, 5.62%); Crystalline
CHCl3); Rf 0.62 (hexane-EtOAc, 90:10); nmax (CHCl3)/cm-1 3065,
3031, 2965, 2878, 1784, 1683, 1602, 1495, 1450, 1394, 1363, 1334,
1250, 1108, 1001, 762; dH(200 MHz; CDCl3) 0.39 (3 H, s, SiMe),
0.40 (3 H, s, SiMe), 0.76 (3 H, d, J 6.6, CHMeAMeB), 0.89 (3 H,
d, J 6.8, CHMeAMeB), 1.91-2.06 (1 H, m, NCHCHMe2), 2.33 (3
H, s, Ar-Me), 5.46 (1 H, d, J 3.2, NCHCHMe2), 7.16-7.66 (16 H,
solid; mp 162–163 ◦C (from hexane-EtOAc); [a]D -5.3 (c 0.87 in
28
EtOH); Rf 0.71 (hexane-EtOAc, 70:30); nmax (CHCl3)/cm-1 3019,
2966, 1780, 1697, 1388, 1376, 1302, 1252, 1215, 1098, 919, 846,
759; dH(200 MHz; CDCl3) 0.04 (6 H, s, 2 ¥ SiMe), 0.32 (6 H, s, 2 ¥
SiMe), 0.87 (6 H, d, J 7.8, 2 ¥ CHMeAMeB), 0.92 (6 H, d, J 7.8,
2 ¥ CHMeAMeB), 1.10-1.51 (2 H, m, 2 ¥ Me2SiCHCH2), 2.27–2.43
(2 H, m, 2 ¥ NCHCHMe2), 2.81 (2 H, dd, J 18.6 and 10.8, 2 ¥
-CHAHBCON), 3.43 (2 H, dd, J 18.6 and 4.4, 2 ¥ -CHAHBCON),
4.17-4.33 (4 H, m, 2 ¥ NCO2CH2CH), 4.37-4.44 (2 H, m, 2 ¥
NCHCHMe2); dC(50 MHz; CDCl3) -2.4 (2 C), 1.1 (2 C), 14.6 (2
C), 17.9 (2 C), 25.8 (2 C), 28.4 (2 C), 38.2 (2 C), 58.4 (2 C), 63.5 (2
C), 154.1 (2 C), 173.7 (2 C); m/z (EI) 483 (M - 15, 5%), 327 (27),
328 (100), 260 (81), 228 (15), 213 (19), 199 (71), 174 (34), 149 (32),
133 (66), 117 (19), 73 (22), 69 (21).
=
m, 2 ¥ Ph, Ar, CH CHCON); dC(50 MHz; CDCl3) -3.2 (2 C),
16.3, 21.4, 21.7, 30.1, 64.4, 89.2, 125.6 (2 C), 125.9 (2 C), 127.9,
128.3 (2 C), 128.5, 128.8 (2 C), 128.8 (2 C), 132.7, 133.2, 133.8 (2
C), 138.2, 139.3, 142.2, 149.8, 152.8, 164.2; m/z (EI) 468 (M - 15,
5%), 424 (16), 337 (21), 262 (14), 222 (34), 207 (100), 167 (40), 149
(55), 129 (22), 105 (24), 91 (16).
1,1,3,3-Tetramethyl-1,3-di-{2-[3-(4S)-3-carbonyl-5,5-diphenyl-4-
isopropyl-2-oxazolidinone]ethenyl}disiloxane 13b
Data for trans-15a: (Found: C, 52.99; H, 7.74; N, 6.21.
C22H38N2O7Si2 requires C, 52.98; H, 7.68; N, 5.62%); Crystalline
solid; mp 141–142 ◦C (from hexane-EtOAc); [a]D27 +152.9 (c 0.90
in EtOH); Rf 0.71 (hexane-EtOAc, 70:30); nmax (CHCl3)/cm-1 3019,
2965, 2877, 1779, 1696, 1487, 1388, 1302, 1251, 1210, 1096, 920,
846, 751; dH(200 MHz; CDCl3) 0.05 (6 H, s, 2 ¥ SiMe), 0.30 (6 H, s,
2 ¥ SiMe), 0.88 (6 H, d, J 7.8, 2 ¥ CHMeAMeB), 0.92 (6 H, d, J 7.8,
2 ¥ CHMeAMeB), 1.15-1.19 (2 H, m, 2 ¥ Me2SiCHCH2), 2.28–2.44
(2 H, m, 2 ¥ NCHCHMe2), 2.82 (2 H, dd, J 17.8 and 10.4, 2 ¥
-CHAHBCON), 3.41 (2 H, dd, J 17.8 and 4.6, 2 ¥ -CHAHBCON),
4.17-4.33 (4 H, m, 2 ¥ NCO2CH2CH), 4.38-4.45 (2 H, m, 2 ¥
NCHCHMe2); dC(50 MHz; CDCl3) -2.3 (2 C), 1.0 (2 C), 14.5 (2
C), 18.0 (2 C), 25.9 (2 C), 28.1 (2 C), 38.1 (2 C), 58.4 (2 C), 63.2 (2
C), 154.0 (2 C), 173.7 (2 C); m/z (EI) 483 (M - 15, 5%), 327 (26),
328 (100), 260 (80), 228 (15), 213 (19), 199 (69), 174 (35), 149 (32),
133 (64), 117 (18), 73 (22), 69 (21).
Following the procedure for the preparation of disiloxane 13a,
oxazolidinone 10b (1.8 g, 3.7 mmol) and trifluoromethanesulfonic
acid (0.98 mL, 11.15 mmol, 3 equiv) at -15 ◦C gave the disiloxane
13b (1.2 g, 81%) as a colourless solid. (Found: C, 68.83; H, 6.59;
N, 3.59. C46H52N2O7Si2 requires C, 68.97; H, 6.54; N, 3.50%);
mp 148–150 ◦C (from hexane-EtOAc); [a]D -193.2 (c 1.03 in
24
CHCl3); Rf 0.52 (hexane-EtOAc, 85:15); nmax (CHCl3)/cm-1 3024,
2965, 2877, 1782, 1683, 1450, 1364, 1335, 1256, 1213, 1176, 1053,
752; dH(200 MHz; CDCl3) 0.18 (6 H, s, 2 ¥ SiMe), 0.19 (6 H, s,
2 ¥ SiMe), 0.77 (6 H, d, J 6.8, 2 ¥ CHMeAMeB), 0.89 (6 H, d, J
7.0, 2 ¥ CHMeAMeB), 1.91-2.06 (2 H, m, 2 ¥ NCHCHMe2), 5.45
(2 H, d, J 3.2, 2 ¥ NCHCHMe2), 7.20-7.62 (24 H, m, 4 ¥ Ph, 2 ¥
=
CH CHCON); dC(50 MHz; CDCl3) 0.2 (4 C), 16.2 (2 C), 21.6 (2
C), 29.9 (2 C), 64.4 (2 C), 89.1 (2 C), 125.4 (4 C), 125.7 (4 C), 127.7
(2 C), 128.1 (4 C), 128.3 (2 C), 128.7 (4 C), 132.7 (2 C), 138.1 (2
C), 142.1 (2 C), 149.2 (2 C), 152.5 (2 C), 164.1 (2 C); m/z (ES) 823
(M + Na, 8%), 801 (M + H, 100).
31
Data for cis-14a: Colourless thick gum; [a]D +58.2 (c 0.67
in EtOH); Rf 0.71 (hexane-EtOAc, 70:30); nmax (CHCl3)/cm-1
2963, 2977, 1780, 1698, 1387, 1302, 1252, 1208, 1097, 10120, 919;
dH(500 MHz; CDCl3) 0.16 (3 H, s, SiMe), 0.17 (3 H, s, SiMe),
0.23 (3 H, s, SiMe), 0.25 (3 H, s, SiMe), 0.88 (6 H, d, J 7.0, 2 ¥
CHMeAMeB), 0.92 (6 H, d, J 7.8, 2 ¥ CHMeAMeB), 1.69-1.73 (1
H, m, Me2SiCHCH2), 1.82-1.86 (1 H, m, Me2SiCHCH2), 2.30–
2.43 (2 H, m, 2 ¥ NCHCHMe2), 2.95 (2 H, dd, J 17.5 and 9.0,
2 ¥ -CHAHBCON), 3.15 (1 H, dd, J 17.5 and 6.0, -CHAHBCON),
3.22 (1 H, dd, J 18.0 and 7.5, -CHAHBCON), 4.18-4.23 (2 H, m,
NCO2CH2CH), 4.26-4.34 (2 H, m, NCO2CH2CH), 4.39-4.42 (1 H,
m, NCHCHMe2), 4.44-4.47 (1 H, m, NCHCHMe2); dC(125 MHz;
CDCl3) -1.3, -1.1, 0.1, 0.5, 14.5, 14.5, 18.0 (2 C), 22.4, 22.9, 28.2,
28.3, 32.9, 33.5, 58.5 (2 C), 63.2, 63.3, 154.1, 154.2, 173.4, 173.6;
Reductive cyclisation of 13b to give trans-14b, trans-15b and
cis-14b
Following the procedure of intramolecular reductive cyclisation
of disiloxane 2a, disiloxane 13b (0.945 g, 1.18 mmol), magnesium
turnings (0.344 g, 14.2 mmol) and TMSCl (1.8 mL, 14.2 mmol)
gave a mixture of trans-14b, trans-15b and cis-14b (0.79 g, 83%).
The residue was crystallised from hexane-ethyl acetate to give
the major trans-15b (0.28 g, 29%). The remaining portion (0.5 g,
54%) consisted of a mixture of all three isomers from which the
individual isomers could not be separated by crystallisation or
chromatography.
4618 | Org. Biomol. Chem., 2009, 7, 4611–4621
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
Data for trans-15b: Solid; mp 93–95 ◦C (from hexane-EtOAc);
[a]D -98.3 (c 0.6 in CHCl3); Rf 0.51 (hexane-EtOAc, 85:15); nmax
180 ◦C (from hexane-EtOAc); [a]D -235.8 (c 1.02 in EtOAc); Rf
0.65 (hexane-EtOAc, 75:25); nmax (CHCl3)/cm-1 3019, 2964, 2879,
2836, 1778, 1683, 16011, 1503, 1465, 1343, 1253, 1201, 1033, 760;
dH(200 MHz; CDCl3) 0.20 (12 H, s, 4 ¥ SiMe), 0.74 (6 H, d, J 6.8,
2 ¥ CHMeAMeB), 0.98 (6 H, d, J 7.2, 2 ¥ CHMeAMeB), 1.69-1.77
(2 H, m, 2 ¥ NCHCHMe2), 2.23 (6 H, s, 2 ¥ Ar-Me), 2.35 (6 H, s,
2 ¥ Ar- Me), 3.49 (12 H, s, 4 ¥ OMe-Ar), 5.85 (2 H, d, J 1.8, 2 ¥
NCHCHMe2), 6.65 (4 H, t, J 9.2, Ar), 6.95-7.10 (4 H, m, Ar),
24
26
(CHCl3)/cm-1 3062, 3029, 2966, 2878, 1783, 1701, 1450, 1369,
1251, 1176, 929, 758; dH(200 MHz; CDCl3) -0.43 (6 H, s, 2 ¥
SiMe), 0.20 (6 H, s, 2 ¥ SiMe), 0.77 (6 H, d, J 6.0, 2 ¥ CHMeAMeB),
0.86 (6 H, d, J 8.0, 2 ¥ CHMeAMeB), 1.00-1.05 (2 H, m, 2 ¥
Me2SiCHCH2), 1.91-2.06 (2 H, m, 2 ¥ NCHCHMe2), 2.65 (2 H,
dd, J 18.6 and 11.0, 2 ¥ -CHAHBCON), 3.32 (2 H, dd, J 18.6 and
3.4, 2 ¥ -CHAHBCON), 5.34 (2 H, d, J 4.0, 2 ¥ NCHCHMe2),
7.26-7.50 (20 H, m, 4 ¥ Ph); dC(50 MHz; CDCl3) -3.0 (2 C), 1.1 (2
C), 16.5 (2 C), 21.5 (2 C), 25.4 (2 C), 29.8 (2 C), 37.6 (2 C), 64.7
(2 C), 89.5 (2 C), 125.5 (4 C), 125.8 (4 C), 127.9 (2 C), 128.3 (4
C), 128.6 (2 C), 128.9 (4 C), 137.9 (2 C), 142.3 (2 C), 153.1 (2 C),
173.3 (2 C); Found: MH+ 803.3507, C46H55N2O7Si2 requires MH+
803.3542; m/z (ES) 825 (M + Na, 6%), 803 (M + H, 63), 279 (100),
132 (33).
=
7.16 (1 H, s, Ar), 7.26 (2 H, d, J 18.6, 2 ¥ CH CHCON), 7.36 (1
H, s, Ar), 7.61 (2 H, d, J 18.6, 2 ¥ CH CHCON), 7.69 (1 H, s,
=
Ar), 7.70 (1 H, s, Ar); dC(50 MHz; CDCl3) 0.1 (4 C), 15.8 (2 C),
20.4 (4 C), 22.4 (2 C), 29.8 (2 C), 55.0 (2 C), 55.5 (2 C), 62.1 (2 C),
88.8 (2 C), 110.8 (2 C), 113.4 (2 C), 126.3 (2 C), 127.4 (2 C), 127.7
(2 C), 128.4 (2 C), 128.6 (2 C), 128.6 (2 C), 128.9 (2 C), 129.8 (2
C), 133.2 (2 C), 148.0 (2 C), 152.4 (2 C), 153.0 (2 C), 155.9 (2 C),
164.2 (2 C); m/z (ES) 999 (M + Na, 19%), 977 (M + H, 15), 500
(100).
Data for trans-14b from the mixture containing about 55% of
trans-15b: dH(200 MHz; CDCl3) 0.03 (6 H, s, 2 ¥ SiMe), 0.20 (6
H, s, 2 ¥ SiMe), 0.72 (6 H, d, J 6.0, 2 ¥ CHMeAMeB), 0.86 (6 H, d, J
8.0, 2 ¥ CHMeAMeB), 0.93-1.05 (2 H, m, 2 ¥ Me2SiCHCH2), 1.91-
2.06 (2 H, m, 2 ¥ NCHCHMe2), 2.74 (2 H, dd, J 19.6 and 11.0, 2 ¥
-CHAHBCON), 3.17 (2 H, dd, J 19.6 and 3.2, 2 ¥ -CHAHBCON),
5.32 (2 H, d, J 4.0, 2 ¥ NCHCHMe2), 7.23-7.50 (20 H, m, 4 ¥ Ph).
Reductive cyclisation of 13c to give trans-14c, trans-15c and cis-14c
Following the procedure of intramolecular reductive cyclisation
of disiloxane 2a, disiloxane 13c (0.695 g, 0.71 mmol), magnesium
turnings (0.21 g, 8.64 mmol) and TMSCl (1.1 mL, 8.68 mmol)
gave a mixture of trans-14c, trans-15c and cis-14c (0.58 g, 83%).
The residue was crystallised from hexane-ethyl acetate to give the
major trans-15c (0.21 g, 30%). The remaining portion (0.37 g,
53%) consisted of a mixture of all three isomers from which the
individual isomers could not be separated.
(4S)-3-trans-(2-dimethyltolylsilyl)acryloyl-4-isopropyl-5,5-di(2-
methoxy-5-methyl)-2-oxazolidinone 10c
Following the procedure for the preparation of 10a, (E)-3-
[dimethyl(tolyl)silyl]propenoic acid 11b (1.02 g, 4.6 mmol), ox-
azolidinone 12c (1.7 g, 4.6 mmol) and n-BuLi (3.1 mL, 1.5 M
solution in hexane, 4.6 mmol) gave N-substituted oxazolidinone
10c (2.4 g, 91%) as a crystalline solid. (Found: C, 71.61; H, 7.38; N,
2.89. C34H41NO5Si requires C, 71.42; H, 7.23; N, 2.45%); mp 160–
Data for trans-15c: Colourless solid; mp 250–252 ◦C (from
hexane-EtOAc); [a]D -135.1 (c 0.6 in CHCl3); Rf 0.63 (hexane-
24
EtOAc, 75:25); nmax (CHCl3)/cm-1 2957, 2926, 2856, 1779, 1695,
1502, 1464, 1372, 1252, 1200, 1032, 924; dH(200 MHz; CDCl3)
-0.20 (6 H, s, 2 ¥ SiMe), 0.34 (6 H, s, 2 ¥ SiMe), 0.74 (6 H, d, J 6.6,
2 ¥ CHMeAMeB), 0.95 (6 H, d, J 7.2, 2 ¥ CHMeAMeB), 1.09-1.14
(2 H, m, 2 ¥ Me2SiCHCH2), 1.61-1.75 (2 H, m, 2 ¥ NCHCHMe2),
2.23 (6 H, s, 2 ¥ Ar-Me), 2.35 (6 H, s, 2 ¥ Ar-Me), 2.74 (2 H, dd,
J 19.0, 11.4, 2 ¥ -CHAHBCON), 3.44 (2 H, dd, J 19.0 and 3.0,
-CHAHBCON), 3.48 (12 H, s, 4 ¥ OMe-Ar), 5.75 (2 H, d, J 2.0,
2 ¥ NCHCHMe2), 6.65 (4 H, dd, J 12.8 and 8.2, Ar), 6.96-7.10
(4 H, m, Ar), 7.21 (1 H, s, Ar), 7.22 (1 H, s, Ar), 7.70 (1 H, s, Ar),
7.71 (1 H, s, Ar); dC(50 MHz; CDCl3) -2.6 (2 C), 1.5 (2 C), 16.0
(2 C), 20.6 (2 C), 20.8 (2 C), 22.4 (2 C), 25.1 (2 C), 29.9 (2 C), 38.1
(2 C), 55.3 (2 C), 56.0 (2 C), 61.7 (2 C), 89.0 (2 C), 111.0 (2 C),
114.1 (2 C), 126.3 (2 C), 126.9 (2 C), 127.9 (2 C), 128.9 (6 C), 129.1
(2 C), 130.1 (2 C), 152.7 (2 C), 153.5 (2 C), 156.4 (2 C), 173.5 (2 C);
Found: MH+ 979.4545, C54H71N2O11Si2 requires MH+ 979.4591;
m/z (ES) 1001 (M + Na, 11%), 979 (M + H, 100), 318 (14), 279
(45), 132 (7).
161 ◦C (from hexane-EtOAc); [a]D -215.8 (c 1.05 in EtOAc); Rf
28
0.69 (hexane-EtOAc, 85:15); nmax (CHCl3)/cm-1 3072, 3035, 3012,
2999, 2964, 2835, 1772, 1683, 1604, 1504, 1465, 1342, 1250, 1201,
1107, 1034, 910, 821, 730; dH(200 MHz; CDCl3) 0.39 (3 H, s,
SiMe), 0.40 (3 H, s, SiMe), 0.73 (3 H, d, J 6.8, CHMeAMeB), 0.97
(3 H, d, J 7.0, CHMeAMeB), 1.67-1.82 (1 H, m, NCHCHMe2),
2.23 (3 H, s, Ar-Me), 2.34 (3 H, s, Ar-Me), 2.36 (3 H, s, Ar-Me),
3.48 (3 H, s, OMe-Ar), 3.49 (3 H, s, OMe-Ar), 5.85 (1 H, d, J
1.8, NCHCHMe2), 6.66 (2 H, dd, J 8.2 and 10.0, Ar), 6.98-7.10
=
(2 H, m, Ar), 7.16-7.70 (8 H, m, Ar, CH CHCON); dC(50 MHz;
CDCl3) -3.1 (2 C), 16.0, 20.7 (2 C), 21.4, 22.6, 30.1, 55.4, 56.0,
62.3, 89.0, 111.0, 113.8, 126.7, 127.6, 128.1, 128.7 (3 C), 128.9,
129.0, 129.1, 130.0, 133.0, 133.9 (3 C), 139.2, 148.4, 152.7, 153.3,
156.2, 164.4; m/z (EI) 571(M+, 3%), 556 (M - 15, 2), 512 (15), 310
(26), 293 (18), 271 (20), 255 (28), 203 (55), 149 (100), 135 (45), 105
(20), 91 (14).
Data for trans-14c from the mixture containing about 5% of
trans-15c: dH(200 MHz; CDCl3) 0.07 (6 H, s, 2 ¥ SiMe), 0.37
(6 H, s, 2 ¥ SiMe), 0.69 (6 H, d, J 6.6, 2 ¥ CHMeAMeB), 0.95 (6 H,
d, J 7.0, 2 ¥ CHMeAMeB), 1.09-1.14 (2 H, m, 2 ¥ Me2SiCHCH2),
1.61-1.75 (2 H, m, 2 ¥ NCHCHMe2), 2.24 (6 H, s, 2 ¥ Ar-Me), 2.34
(6 H, s, 2 ¥ Ar-Me), 2.93 (2 H, dd, J 19.0, 11.2, 2 ¥ -CHAHBCON),
3.12 (2 H, dd, J 19.0 and 4.0, -CHAHBCON), 3.46 (6 H, s, 2 ¥
OMe-Ar), 3.48 (6 H, s, 2 ¥ OMe-Ar), 5.76 (2 H, d, J 1.5, 2 ¥
NCHCHMe2), 6.64 (4 H, dd, J 12.0 and 8.4, Ar), 6.96-7.10 (4 H,
m, Ar), 7.14 (1 H, s, Ar), 7.15 (1 H, s, Ar), 7.66 (1 H, s, Ar), 7.67
(1 H, s, Ar).
1,1,3,3-Tetramethyl-1,3-di-{2-[3-(4S)-3-carbonyl-5,5-di(2-
methoxy-5-methyl)-4-isopropyl-2-oxazolidinone]-
ethenyl}disiloxane 13c
Following the procedure for the preparation of disiloxane 13a,
oxazolidinone 10c (1.32 g, 2.3 mmol) and TfOH (0.51 mL,
5.8 mmol, 2.5 equiv) at -15 ◦C gave the disiloxane 13c (0.81 g,
72%) as a colourless solid. (Found: C, 66.70; H, 7.17; N, 2.92.
C54H68N2O11Si2 requires C, 66.36; H, 7.01; N, 2.87%); mp 179–
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4611–4621 | 4619
©

View Article Online
(3S,4S)-Dihydroxyadipic-c,c¢-dilactone (-)-16
6 (a) M. M. Baizer and J. D. Anderson, J. Electrochem. Soc., 1964, 111,
223; (b) A. J. Fry, in Synthetic Organic Electrochemistry, John Wiley
and Sons, New York, NY, 2nd edn., 1989, pp. 208.
Hydrogen peroxide (0.6 mL, 30%) was added to a stirred mixture
of trans-14a (0.15 g, 0.3 mmol) and KHF2 (0.14 g, 1.8 mmol) in
THF/MeOH (6 mL, 1:1). After 24 h at 60 ◦C, H2O2 (0.3 mL)
was added to the reaction mixture followed by addition of
THF/MeOH (2 mL, 1:1). After 15 h, the solvent was evaporated
under reduced pressure. The white residue was triturated with
hot EtOAc and filtered. The filtrate on evaporation gave the
oxazolidinone (35 mg, 90%). The solid residue was taken up in
0.2 molar methanolic HCl (10 mL) and evaporated. The residue
was triturated with ethyl acetate and filtered. The filtrate was
evaporated under reduced pressure and the residue was dissolved
in THF (2 mL), TsOH (2 mg, 0.01 mmol) was added into it and the
mixture was heated at 55 ◦C for 12 h. Sodium bicarbonate (3 mg)
was added and the reaction mixture was diluted with hot EtOAc
and filtered, then the filtrate was evaporated to give the lactone
7 (a) E. L. Totton, N. C. Camp, III, G. M. Cooper, B. D. Haywood and
D. P. Lewis, J. Org. Chem., 1967, 32, 2033; (b) K. W. Bowers, R. W.
Giese, J. Grimshaw, H. O. House, N. H. Kolodny, K. Kronberger and
D. K. Roe, J. Am. Chem. Soc., 1970, 92, 2783; (c) H. O. House, R. W.
Giese, K. Kronberger, J. P. Kaplan and J. P. Simeone, J. Am. Chem.
Soc., 1970, 92, 2800.
8 K. Takaki, F. Beppu, S. Tanaka, Y. Tsubaki, T. Jintoku and Y. Fujiwara,
J. Chem. Soc., Chem. Commun., 1990, 516.
9 (a) Y. Liu, N. Dai, Y. Qi and S. Zhang, Synth. Commun., 2009, 39, 799;
(b) For a review, see: B. K. Banik, Eur. J. Org. Chem., 2002, 2431.
10 D. Y. Jung and Y. H. Kim, Synlett, 2005, 3019.
11 L. Zhou, D. Shi, Y. Gao, W. Shen, G. Dai and W. Chen, Tetrahedron
Lett., 1997, 38, 2729.
12 (a) J. Inanaga, Y. Handa, T. Tabuchi, K. Otsubo, M. Yamaguchi and
T. Hanamoto, Tetrahedron Lett., 1991, 32, 6557; (b) S. Kanemasa, H.
Yamamoto and S. Kobayashi, Tetrahedron Lett., 1996, 37, 8505; (c) T.
Kikukawa, T. Hanamoto and J. Inanaga, Tetrahedron Lett., 1999, 40,
7497.
13 (a) I. Shinohara, M. Okue, Y. Yamada and H. Nagaoka, Tetrahedron
Lett., 2003, 44, 4649; (b) A. Cabrera, R. L. Lagadec, P. Sharma, J. L.
Arias, R. A. Toscano, L. Velasco, R. Gavino, C. Alvarez and M.
Salmon, J. Chem. Soc., Perkin Trans. 1, 1998, 3609.
14 M. E. Osborn, J. F. Pegues and L. A. Paquette, J. Org. Chem., 1980, 45,
167.
15 (a) H. E. Bode, C. G. Sowell and R. D. Little, Tetrahedron Lett., 1990,
31, 2525; (b) R. D. Little, D. P. Fox, L. V. Hijfte, R. Dannecker, G.
Sowell, R. L. Wolin, L. Mones and M. M. Baizer, J. Org. Chem., 1988,
53, 2287; (c) D. P. Fox, R. D. Little and M. M. Baizer, J. Org. Chem.,
1985, 50, 2202; (d) L. Moens, M. M. Baizer and R. D. Little, J. Org.
Chem., 1986, 51, 4497.
16 J. Yang, G. A. N. Felton, N. L. Bauld and M. J. Krische, J. Am. Chem.
Soc., 2004, 126, 1634.
17 S. R. Angle and J. D. Rainier, J. Org. Chem., 1992, 57, 6883.
18 (a) G. H. Lee, E. B. Choi, E. Lee and C. S. Pak, J. Org. Chem., 1994,
59, 1428; (b) For a review, see: G. H. Lee, I. K. Youn, E. B. Choi, H. K.
Lee, G. H. Yon, H. C. Yang and C. S. Pak, Curr. Org. Chem., 2004, 8,
1263.
(-)-16 (44 mg, 100%) as a solid. mp 122–124 ◦C (hexane-EtOAc)
◦
(lit.42 mp 122–123 C); [a]D -145.3 (c 0.64 in H2O) (lit.42; [a]D
=
23
19
+143 2.5, c 0.785, H2O for the antipode); Rf 0.57 (hexane-EtOAc,
2:8); nmax (CHCl3)/cm-1 3023, 2993, 2958, 1783, 1401, 1343, 1309,
1191, 1165, 1051; dH(200 MHz; CDCl3) 2.83-3.04 (4 H, m, 2 ¥
CH2), 5.18-5.24 (2 H, m, 2 ¥ CH); dC(50 MHz; CDCl3) 35.1 (2 C),
78.3 (2 C), 172. 9 (2 C).
(3R,4R)-Dihydroxyadipic-c,c¢-dilactone (+)-16
Following the procedure for conversion of trans-14a to (--)-16,
disiloxane trans-15a (0.1 g, 0.2 mmol) and H2O2 (0.7 mL, 30%)
gave lactone (+)-16 (25 mg, 88%)◦as a solid. mp 121–123 ◦C
25
(hexane-EtOAc) (lit.42 mp 122–123 C); [a]D +142.11 (c 0.38 in
H2O) (lit.42; [a]D = +143 2.5, c 0.785, H2O); Rf 0.57 (hexane-
19
19 S. P. Chavan and K. S. Ethiraj, Tetrahedron Lett., 1995, 36,
EtOAc, 20:80); nmax (CHCl3)/cm-1 3023, 2993, 2958, 1783, 1401,
1343, 1309, 1191, 1165, 1051, 927, 836; dH(200 MHz; CDCl3)
2.83-3.04 (4 H, m, 2 ¥ CH2), 5.18-5.24 (2 H, m, 2 ¥ CH);
dC(50 MHz; CDCl3) 35.1 (2 C), 78.3 (2 C), 172. 9 (2 C). Recovery
of oxazolidinone 12a (27 mg, 80%). This compound was also
obtained by Fleming–Tamao oxidation of trans-15b in 85% yield.
Recovery of oxazolidinone 12b was 75%. This compound was also
obtained by Fleming–Tamao oxidation of trans-15c in 84% yield.
Recovery of oxazolidinone 12c was 70%.
2281.
20 (a) G. Pandey and S. Hajra, Angew. Chem., Int. Ed. Engl., 1994, 33,
1169; (b) G. Pandey, S. Hajra and M. K. Ghorai, Tetrahedron Lett.,
1994, 35, 7837; (c) G. Pandey, S. Hajra, M. K. Ghorai and K. R.
Kumar, J. Am. Chem. Soc., 1997, 119, 8777; (d) G. Pandey, S. Hajra
and M. K. Ghorai, J. Org. Chem., 1997, 62, 5966; (e) G. Pandey, M. K.
Ghorai and S. Hajra, Tetrahedron Lett., 1998, 39, 1831; (f) G. Pandey,
A. L. Gaikwad and S. R. Gadre, Tetrahedron Lett., 2006, 47, 701.
21 (a) E. J. Enholm and K. S. Kinter, J. Org. Chem., 1995, 60, 4850; (b) E. J.
Enholm and K. S. Kinter, J. Am. Chem. Soc., 1991, 113, 7784; (c) D. S.
Hays and G. C. Fu, J. Org. Chem., 1996, 61, 4.
22 (a) S. K. Ghosh, R. Singh and G. C. Singh, Eur. J. Org. Chem., 2004,
4141; (b) R. Singh, G. C. Singh and S. K. Ghosh, Tetrahedron Lett.,
2005, 46, 4719; (c) R. Singh, G. C. Singh and S. K. Ghosh,, Eur. J. Org.
Chem., 2007, 5376.
Notes and references
23 (a) C. M. Jensen, K. B. Lindsay, R. H. Taaning, J. Karaffa, A.-M.
Hansen and T. Skrydstrup, J. Am. Chem. Soc., 2005, 127, 6544; (b) R. H.
Taaning, L. Thim, J. Karaffa, A. C. Campana, A.-M. Hansen and T.
Skrydstrup,, Tetrahedron, 2008, 64, 11884.
24 (a) M. Shabangi and R. A. Flowers, II, Tetrahedron Lett., 1997, 38,
1137; (b) P. W. Atkins, Physical Chemistry, ELBS, Oxford, Fifth Ed,
pp. C20.
1 (a) For a review on silicon controlled stereoselective reactions, see: I.
Fleming, A. Barbero and D. Walter, Chem. Rev., 1997, 97, 2063; (b) For
usefulness of b-silyl carbonyl compounds, see: I. Fleming, in Science of
Synthesis, ed. I. Fleming, Thieme, Stuttgart, 2002, vol. 4, pp. 927.
2 (a) A. Barbero, D. C. Blakemore, I. Fleming and R. N. Wesley, J. Chem.
Soc., Perkin Trans. 1, 1997, 1329; (b) M. Ahmar, C. Duyck and I.
Fleming, J. Chem. Soc., Perkin Trans. 1, 1998, 2721.
3 (a) P. Girard, J. L. Namy and H. B. Kagan, J. Am. Chem. Soc., 1980,
102, 2693; (b) K. Gopalaiah and H. B. Kagan, New J. Chem., 2008, 32,
607; (c) H. B. Kagan, Tetrahedron, 2003, 59, 10351; (d) G. A. Molander
and C. R. Harris, Chem. Rev., 1996, 96, 307.
25 H. Maekawa, M. Sakai, T. Uchida, Y. Kita and I. Nishiguchi,
Tetrahedron Lett., 2004, 45, 607.
26 (a) R. Nomura, T. Matsuno and T. Endo, J. Am. Chem. Soc., 1996, 118,
11666; (b) H. C. Aspinall, N. Greeves and C. Valla, Org. Lett., 2005, 7,
1919; (c) F. Helion and J.-L. Namy, J. Org. Chem., 1999, 64, 2944.
27 E. J. Corey and G. Z. Zheng, Tetrahedron Lett., 1997, 38, 2045.
28 K. Mikami, M. Terada and H. Matsuzawa, Angew. Chem., Int. Ed.,
2002, 41, 3554.
4 (a) I. Fleming and S. K. Ghosh, J. Chem. Soc., Chem. Commun., 1992,
1775; (b) I. Fleming and S. K. Ghosh, J. Chem. Soc., Chem. Commun.,
1992, 1777; (c) I. Fleming and S. K. Ghosh, J. Chem. Soc., Perkin Trans.
1, 1998, 2711.
29 (a) D. A. Evans, Aldrichimica Acta, 1982, 15, 23; (b) D. A. Evans
and A. S. Kim, in Encyclopedia of Reagents for Organic Synthesis, ed.
L. A. Paquette, Wiley, NY, 1995, vol.11, pp. 345; (c) D. Ager, I. Prakash
and D. R. Schaad, Chem. Rev., 1996, 96, 835.
5 (a) I. Fleming and S. K. Ghosh, J. Chem. Soc., Chem. Commun., 1994,
2285; (b) I. Fleming and S. K. Ghosh, J. Chem. Soc., Chem. Commun.,
1994, 2287; (c) I. Fleming and S. K. Ghosh, J. Chem. Soc., Perkin Trans.
1, 1998, 2733.
4620 | Org. Biomol. Chem., 2009, 7, 4611–4621
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
30 (a) D. A. Evans and A. E. Weber, J. Am. Chem. Soc., 1986, 108, 6757;
(b) D. A. Evans, K. T. Chapman and J. Bisaha, J. Am. Chem. Soc., 1988,
110, 1238.
31 D. A. Evans, M. D. Ennis and D. J. Mathre, J. Am. Chem. Soc., 1982,
104, 1737.
32 M. P. Sibi and S. Manyem, Tetrahedron, 2000, 56, 8033.
33 N. Kise, S.-I. Mashiba and N. Ueda, J. Org. Chem., 1998, 63, 7931.
34 M. P. Sibi, S. Manyem and J. Zimmerman, Chem. Rev., 2003, 103, 3263.
35 (a) S. G. Davies and H. J. Sanganee, Tetrahedron: Asymmetry, 1995,
6, 671; (b) S. D. Bull, S. G. Davies, A. C. Garner, D. Kruchinin, M.-S.
Key, P. M. Roberts, E. D. Savory, A. D. Smith and J. E. Thomson, Org.
Biomol. Chem., 2006, 4, 2945.
40 I. Fleming, Chemtracts-Org. Chem., 1996, 9, 1.
41 K. Tamao, N. Ishida, Y. Ito and M. Kumada, Org. Synth., 1990, 69,
96.
42 T. Posternak and J.-P. Susz, Helv. Chim. Acta, 1956, 39, 2032.
43 M. Hizuka, N. Hayashi, T. Kamashita, H. Suemune and K. Sakai,
Chem. Pharm. Bull., 1988, 36, 1550.
44 M. Tanaka, T. Murakami, H. Suemune and K. Sakai, Heterocycles,
1992, 33, 697.
45 M. Hizuka, C. Fang, H. Suemune and K. Sakai, Chem. Pharm. Bull.,
1989, 37, 1185.
46 B. Anorbe, V. S. Martin, J. M. Palazone and J. M. Trujillo, Tetrahedron
Lett., 1986, 27, 4991.
36 T. Hintermann and D. Seebach, Helv. Chim. Acta, 1998, 81, 2093.
37 (a) C. L. Gibson, K. Gillon and S. Cook, Tetrahedron Lett., 1998, 39,
6733; (b) S. D. Bull, S. G. Davis, S. Jones, M. E. C. Polywka, R. S.
Prasad and H. J. Sanganee, Synlett, 1998, 519.
38 N. Chaubey, S. M. Date and S. K. Ghosh, Tetrahedron: Asymmetry,
2008, 19, 2721.
47 (a) C. A. Moustakis, J. Viala, J. Capdevila and J. R. Falck, J. Am. Chem.
Soc., 1985, 107, 5283; (b) F. Mosset, P. Yadagiri, S. Lumin, J. Capdevila
and J. R. Falck, Tetrahedron Lett., 1986, 27, 6035; (c) M. D. Ennis and
M. E. Base, Tetrahedron Lett., 1986, 27, 6031.
48 J. Kiegiel, J. Nowacki, A. Tarnowska, M. Stachurska and J. Jurczak,
Tetrahedron Lett., 2000, 41, 4003.
39 M. Brenner, L. L. Vecchia, T. Leutert and D. Seebach, Org. Synth.,
2002, 80, 57.
49 K. Takeshita, Y. Seki, K. Kawamoto, S. Murai and N. Sonoda, J. Org.
Chem., 1987, 52, 4864.
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 4611–4621 | 4621
©